Posterior (from the back) spinal surgery requires that the patient be placed in the prone position. However, there are a great number of problems associated with just lying the patient flat out in the face down position.
Starting at the head end of the patient, the patient's neck will be either hyperextended, hyperrotated, or a combination thereof. The weight of the patient's head will come to rest on the periorbital region causing periorbital compression and edema and if continued for too long, eye damage. The weight of the torso lying over the chest increases the work of respiration and necessitates high ventilator drive pressures which cause the lung to transudate fluid (the pressure squeezes fluid from the lungs) and may lead to pulmonary edema. Furthermore, the pressure across the chest increases the pressure on the superior venae cava (the largest vein in the body which returns the blood to the heart) which results in a backup of pressure down the line and increased venous pressure in the spine, and therefore increased surgical bleeding. Similarly, and even more directly, pressure across the abdomen is directly transmitted via valveless connections to the spine and again results in increased bleeding at the spinal surgery site. Finally, the extended hip position produces a hyperlordosis (increased concavity) of the lumbar spine and shingling of the lamina producing an impediment to the surgery itself.
A significant improvement over the prone position can be obtained by the use of a spinal surgery frame as depicted in FIG. 8. The spinal surgery frame attaches to the operating room table and holds the patient in a modified half-seated, half-kneeling position.
A further improvement can be realized by the addition of a further support placed beneath the chest area of the patient which would allow the neck to fall into gentle flexion. Excessive neck flexion can be reduced by placing a soft pad beneath the patient's forehead which also is beneficial in that the face is then suspended, avoiding the problem of contact pressure to the eye area. Additionally, the use of the support beneath the chest returns the spine back into the horizontal position, facilitating surgery.
Unfortunately, there are also disadvantages associated with the use of conventional chest supports. First, there is the problem of pressure applied against the skin. Secondly, there is the problem of the pressure across the chest in general which increases the superior venae cava pressure and causes bleeding. Thirdly, when the chest is supported but the arms are not, then the large nerves passing from the chest area to the arm area, the brachial plexi, may be stretched, causing neurological injury.
At the present time, folded blankets or stacks of foam sheeting are generally used to support the chest. Also, larger rectangular foam blocks have been used by themselves. Also, a rectangular foam block attached to an ordinary automobile scissors jack has been used to elevate the pad. However, these are less than ideal.